1. Field of the Invention
The present invention relates to a sheet metal formed thereon with a number of spaced projections (for example, suitable for use as a separator in fuel batteries) and a manufacturing method of the same.
2. Discussion of the Prior Art
There has been provided a sheet metal of less than 0.5 mm in thickness formed thereon with a number of spaced projections each of 2-3 mm in diameter and 0.4-0.6 mm in height and spaced in distance of 2-5 mm. In a manufacturing process of the sheet metal, as disclosed in Japanese Patent Laid-open Publication 11-167927, a sheet metal of stainless steel, aluminum Or copper is placed between upper and lower dies in the form of male and female dies and pressed by a half die cutting to form the spaced projections thereon. In the pressing process, a minimum space between the dies in a closed condition is set to become equal to the thickness of the sheet metal.
In the sheet metal pressed by the half die cutting, cracks will occur in the sheet metal and shear drops will occur at each shoulder or root of the projections. In addition, the sheet metal warps in its entirety due to the reaction after the pressing process. For this reason, it is very difficult to enhance the yield of the sheet metal in a reliable manner.
It is, therefore, a primary object of the present invention to provide a sheet metal formed thereon with a number of spaced projections and a manufacturing method of the same capable of forming the spaced projections without causing any crack and warp and any shear drops at each shoulder and root of the projections described above.
According to the present invention, the object is accomplished by providing a sheet metal formed thereon with a number of spaced projections, wherein the projections are formed by the steps of positioning the sheet metal between a female die formed with a number of spaced recesses at one surface thereof and a male die formed with a concavity to be slidably coupled with the female die and a number of spaced projections located at the bottom of the concavity to correspond with the recesses of the female die and pressing the sheet metal under existence of hydraulic fluid between the sheet metal and the concavity of the male die.
According to an aspect of the present invention there is provided a manufacturing method of a sheet metal formed thereon with a number of spaced projections in use of a hydraulic press machine having an upper die in the form of a female die formed with a number of spaced recesses at the bottom surface thereof and a lower die in the form of a male die formed with a concavity to be slidably coupled with the female die and a number of spaced projections located at the bottom of the concavity to correspond with the recesses of the female die, comprising the steps of positioning a sheet metal on an upper end surface of the lower die in such a manner as to prevent entry of the air into the concavity of the lower die in a condition where the concavity bas been filled with hydraulic fluid; moving down a blank holder placed at the outer circumference of the upper die to fixedly retain the sheet metal in position on the upper end surface of the lower die, moving down the upper die in a condition where hydraulic pressure between the concavity of the lower die and the sheet metal is maintained at a high pressure and inserting the upper die into the concavity of the lower die until it arrives at a position slightly higher than a lower dead point; and moving down the upper die in a condition where the hydraulic fluid is discharged from the concavity of the lower die and insert the upper die into the concavity of the lower die until it arrives near the lower dead point.
According to another aspect of the present invention, there is provided a manufacturing method of a sheet metal formed thereon with a number of spaced projections in use of a hydraulic press machine having an upper die in the form of a male die formed with a concavity and a number of spaced projections located at the bottom of the concavity and a lower die in the form of a female die formed at the upper surface thereof with a number of spaced recesses corresponding with the projections of the male die and placed to be slidably coupled within the concavity of the male die, comprising the steps of positioning a sheet metal on an upper end surface of the lower die; moving down a blank holder placed at the outer circumference of the upper die to fixedly retain the peripheral portion of the sheet metal in position on the upper end surface of the lower die; moving down the upper die and retaining it in engagement with the sheet metal; supplying hydraulic fluid into the concavity of the upper die in such a manner as to prevent entry of the air into the concavity of the upper die in a condition where the concavity has been filled with hydraulic fluid; raising the lower die in a condition where hydraulic pressure between the concavity of the upper die and the sheet metal is maintained at a high pressure and inserting the lower die into the concavity of the upper die until it arrives at a position slightly lower than an upper dead point; and raising the lower die in a condition where the hydraulic fluid is discharged from the concavity of the upper die and inserting the lower die into the concavity of the upper die until it arrives near the upper dead point.